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| United States Patent |
5,710,084
|
|
Nojima
, et al.
|
January 20, 1998
|
Catalysts for cleaning exhaust gases
Abstract
A catalyst for cleaning exhaust gases has a first catalyst layer having as
an active metal on an elemental support at least one noble metal selected
from the group consisting of platinum, rhodium and palladium and a second
catalyst layer having iridium as an active metal which is provided as a
overlayer on the first catalyst layer.
| Inventors:
|
Nojima; Shigeru (Hiroshima, JP);
Iida; Kouzo (Hiroshima, JP)
|
| Assignee:
|
Mitsubishi Jukogyo Kabushiki Kaisha (Tokyo, JP)
|
| Appl. No.:
|
514415 |
| Filed:
|
August 11, 1995 |
Foreign Application Priority Data
| Current U.S. Class: |
502/66; 502/64; 502/71; 502/74; 502/77 |
| Intern'l Class: |
B01J 029/06 |
| Field of Search: |
502/64,66,71,74,77
|
References Cited
U.S. Patent Documents
| 3702886 | Nov., 1972 | Argauer et al. | 423/705.
|
| 5164350 | Nov., 1992 | Abe et al. | 502/66.
|
| Foreign Patent Documents |
| 0 485 180 A1 | May., 1992 | EP.
| |
| 6-71181 | Mar., 1994 | JP.
| |
| 6-296870 | Oct., 1994 | JP.
| |
| 7-80315 | Mar., 1995 | JP.
| |
| 7-88378 | Apr., 1995 | JP.
| |
| 7-136463 | May., 1995 | JP.
| |
Other References
Database WPI, Week 9347, Derwent Publications Ltd., London, GB, AN
93-373729 and JP-A-05 277 368 (TOYO KOGYO), 26 Oct. 1992, abstract only.
Database WPI, Week 9216, Derwent Publications Ltd., London, GB, AN
92-129097 and JP-A-04 074 534 (Nissan Motor), 9 Mar. 1992, abstract only.
European Search Report 95 85 0139 (Nov. 24, 1995).
|
Primary Examiner: Lewis; Michael
Assistant Examiner: Dunn, Jr.; Thomas G.
Attorney, Agent or Firm: Morrison & Foerster LLP
Claims
What is claimed is:
1. A catalyst for cleaning exhaust gases comprising a first catalyst layer
having as an active metal on a support at least one noble metal selected
from the group consisting of platinum, rhodium and palladium and a second
catalyst layer consisting essentially of iridium as an active metal is
provided as an overlayer on the first catalyst layer, wherein
the iridium in the second catalyst layer is in a carrier, said carrier is a
crystalline silicate which is represented by the following formula by
molar ratio as dehydrated:
(1.+-.0.8)R.sub.2 O.›aM.sub.2 O.sub.3.bM'O.cAl.sub.2 O.sub.3 !.ySiO.sub.2
wherein, R denotes an alkali metal ion, a hydrogen ion, or a mixture of an
alkali metal ion and a hydrogen ion, M denotes at least one elemental ion
selected from the group consisting of VIII group elements, rare earth
elements, titanium vanadium, chromium, niobium, antimony or gallium, M'
denotes an alkaline earth metal ion of magnesium, calcium, strontium or
barium, a>0, 20>b>0, a+c=1, and 3000>y>11.
Description
FIELD OF THE INVENTION AND RELATED ART STATEMENT
The present invention relates to a catalyst for cleaning exhaust gases
containing nitrogen oxides (hereinafter abbreviated as NOx), carbon
monoxide (CO) and hydrocarbons (HC).
In the automobile exhaust gas disposal, NOx is generally cleaned within a
very limited region around the logical air/fuel ratio by a catalyst while
utilizing CO and HC contained in the exhaust gas. However, in cases of
exhaust gas disposal of lean burn gasoline engines and diesel engines,
denitration is prevented completely when using a conventional catalyst
because of an excessively large amount of oxygen in the exhaust gas.
Recently, crystalline silicate catalysts containing cobalt or copper have
been proposed as catalysts capable of cleaning NOx even in an excessive
oxygen atmosphere.
However, these catalysts suffer problems of deterioration due to heat,
water vapor and sulfur dioxide in the exhaust gas, although they exhibit
satisfactory performance at the initial stage of the reaction.
We have already found after making much effort to obtain a catalyst capable
of overcoming the problems mentioned above that a catalyst on which
iridium is supported is a highly active and durable catalyst (Japanese
Patent Application Numbers H5-26369, H5-100698, H5-228382 and H5-287986).
Nevertheless, the catalyst supporting iridium provides a denitration rate
which is not sufficient when applied to a practical car driving because of
the limited cleaning ability against CO and HC at a low exhaust gas
temperature of 300.degree. C. or lower.
OBJECT AND SUMMARY OF THE INVENTION
An objective of the present invention is to provide a catalyst for cleaning
exhaust gases which exhibits denitration performance not only at a high
temperature but also at a temperature as low as 300.degree. C. or lower.
An aspect of the present invention is a catalyst for cleaning exhaust gases
comprising a first catalyst layer having as an active metal on an
elemental support at least one noble metal selected from the group
consisting of platinum, rhodium and palladium on which a second catalyst
layer having iridium as an active metal is provided as a overlayer.
The catalyst for cleaning exhaust gases according to the present invention
is a highly durable and stable catalyst, which can be utilized as an
exhaust gas cleaning catalyst for a lean burn gasoline engine as well as a
diesel engine.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
A carrier for carrying iridium as an active metal in the second layer
catalyst according to the present invention is a crystalline silicate
which has a X-ray diffraction pattern shown in Table A in the
specification and which is represented by the formula in the molar ratio
as dehydrated: (1.+-.0.8)R.sub.2 O. ›aM.sub.2 O.sub.3.bM'O.cAl.sub.2
O.sub.3 !.ySiO.sub.2 wherein R denotes an alkaline metal ion and/or
hydrogen ion, M denotes at least one elemental ion selected from the group
consisting of VIII group elements, rare earth element, titanium, vanadium,
chromium, niobium, antimony or gallium, M' denotes an alkaline earth metal
ion of magnesium, calcium, strontium or barium, a>0, 20>b.gtoreq.0, a+c=1
and 3000>y>11.
TABLE A
______________________________________
Lattice spacing (interstitial distance)
(d value) Relative strength
______________________________________
11.2 .+-. 0.3 VS
10.0 .+-. 0.3 VS
6.7 .+-. 0.2 W
6.4 .+-. 0.2 M
6.0 .+-. 0.2 M
5.7 .+-. 0.2 W
5.6 .+-. 0.2 M
4.6 .+-. 0.1 W
4.25 .+-. 0.1 M
3.85 .+-. 0.1 VS
3.75 .+-. 0.1 S
3.65 .+-. 0.1 S
3.3 .+-. 0.1 M
3.05 .+-. 0.1 W
3.0 .+-. 0.1 M
______________________________________
VS: Very strong
S: Strong
M: Medium
W: Weak
(Xray source: Cu K.alpha.)
A preferable example of the carrier for carrying iridium as an active metal
in the second catalyst layer according to the present invention other than
the silicate mentioned above is one or more substances selected from the
group consisting of simple oxides such as .gamma.-alumina,
.theta.-alumina, silica, zirconia and titania, complex oxides such as
alumina.zirconia, zirconia.titania and alumina.titania, a solid strong
acid sulfate-containing zirconia (obtained by immersing zirconium
hydroxide in 1N sulfuric acid for about 1 hour at room temperature
followed by filtration, drying and sintering) as well as a series of
zeolites such as zeolite type Y, silicalite (a zeolite having a pentasil
structure cosisting only of Si and O), zeolite type A and mordenite.
A carrier for carrying as the first layer catalyst of an active metal,
which is at least one noble metal selected from the group consisting of
platinum, rhodium and palladium, according to the present invention may be
any of those which can be used as a carrier for a standard catalyst, and
.gamma.-alumina is generally preferred.
The thickness of the coating of the first catalyst layer on the elemental
support is within the range from 1 to 300 .mu.m, preferably 5 to 100
.mu.m, and that of the second catalyst layer is within the range from 1 to
300 .mu.m, preferably 3 to 200 .mu.m. At least one noble metal selected as
the first layer catalyst from the group consisting of platinum, rhodium,
and palladium and iridium as the second layer catalyst are supported on
respective carriers preferably by means of an ion exchange method or an
impregnation method. The noble metal of the first catalyst layer is coated
in an amount of 0.05 to 5 g, and the iridium of the second catalyst layer
is coated in an amount of 0.03 to 10 g, both per 1 L of the elemental
support (generally a coagulate support but any heat-resistant ceramic is
acceptable).
In the catalyst according to the present invention, for the purpose of
achieving the denitrating activity covering a wider range of low
temperature, the catalyst layer carrying at least one noble metal selected
from the group consisting of platinum, rhodium and palladium is provided
beneath the layer carrying iridium.
Thus, the first catalyst layer having as an active metal at least one noble
metal selected from the group consisting of platinum, rhodium and
pallatium is provided on the elemental support, and then the second
catalyst layer having iridium as an active metal is provided as a
overlayer to form a multilayer catalyst.
When applied to an exhaust gas at a temperature of about 250.degree. C. or
higher, no denitration can be effected only by the second layer
iridium-carrying catalyst because there is no burning of CO or HC.
However, in the case where the catalyst carrying at least one noble metal
selected from the group consisting of platinum, rhodium and palladium is
provided as the first layer catalyst, sufficient burning of CO and HC at
250.degree. C. is effected, resulting in the increase in the temperature
of the second layer iridium-carrying catalyst up to the active temperature
range, whereby exhibiting the denitration performance.
In addition, the denitration performance can be obtained continuously from
the exhaust gas temperature ranging from 200.degree. C. to a higher
temperature since platinum, rhodium and palladium can exhibit denitration
activity in association with the burning of CO and HC at a temperature as
low as 200.degree. to 300.degree. C. (Japanese Patent Application Number
H4-230700). On the other hand, at a high exhaust gas temperature of
400.degree. C. or higher, the performance of the second iridium-carrying
catalyst layer becomes predominant, and the first catalyst layer scarcely
affects the reaction, thereby maintaining the high performance.
The exhaust gas containing NOx, CO and HC is cleaned by a catalyst which
carries iridium as the second layer catalyst in the reactions represented
by the formulae shown below.
##STR1##
*1)C.sub.3 H.sub.6 is used as a representative of hydrocarbons (HC).
*2)CH.sub.2 O is used as a representative of oxygen-containing
hydrocarbons.
In the reactions shown above, formula (1) shows the activation of HC,
formula (2) shows the burning of HC, formula (3) shows the denitration,
and formula (4) shows the burning of CO.
EXAMPLE 1
Preparation of Catalyst
5616 g of water glass #1 (SiO.sub.2 : 30%) was dissolved in 5429 g of water
to yield solution A. Separately, 718.9 g of aluminum sulfate, 110 g of
ferric chloride, 47.2 g of calcium acetate, 262 g of sodium chloride and
2020 g of concentrated hydrochloric acid were dissolved together in 4175 g
of water to yield solution B. Solution A and solution B were mixed and
stirred thoroughly to yield a slurry at pH8. These two solutions were fed
keeping the pH as constant as possble at 8. Namely, solution A was fed at
11045/30=368 g/min., whereas Solution B was fed at 7333/30=244 g/min. so
that the pH was kept at 8. The slurry thus obtained was charged in a 20 L
autoclave, to which 500 g of tetrapropyl ammonium bromide was added and
the mixture was subjected to hydrothermal synthesis at 160.degree. C. for
72 hours. After synthesis, washing with water, drying and sintering for 3
hours at 500.degree. C., crystalline silicate 1 was obtained. Crystalline
silicate 1 thus obtained is represented in a molar ratio (excluding
crystal water) by the formula shown below and has the crystal structure
characterized by the X-ray diffraction pattern shown in Table A.
0.5Na.sub.2 O.0.5H.sub.2 O.›0.8Al.sub.2 O.sub.3.0.2Fe.sub.2
O.sub.3.0.25CaO!.25SiO.sub.2
Crystalline silicate 1 obtained above was subjected to NH.sub.4 ion
exchange by stirring with 4N aqueous solution of NH.sub.4 Cl at 40.degree.
C. for 3 hours. After the ion exchange, the silicate was washed and dried
at 100.degree. C. for 24 hours and sintered at 400.degree. C. for 3 hours
to obtain crystalline silicate 1 of type H.
100 g of .gamma.-alumina was immersed in an aqueous solution of chloro
platinic acid (H.sub.2 PtCl.sub.6.6H.sub.2 O: 2.66 g/100 cc) and kept at
120.degree. C. to evaporate to dryness, and then purged with nitrogen for
3 hours at 500.degree. C. to yield powder catalyst 1.
On the other hand, 100 g of crystalline silicate 1 was immersed in an
aquelous solution of chloroiridic acid (H.sub.2 IrCl.sub.6 : 2.1 g/100 cc)
and kept at 120.degree. C. to evaporate to dryness, and then purged with
nitrogen for 3 hours at 500.degree. C. to yield powder catalyst 1'.
Preparation of Honeycomb Catalyst
Then, to mixtures of 100 parts each of powder catalysts 1 and 1', 3 parts
of alumina sol and 55 parts of silica sol (20% SiO.sub.2) as binders and
200 parts of water were added, and the mixtures were stirred thoroughly to
yield slurries of catalysts 1 and 1' for wash coats. Then a monolith
support for coagulate (400-cell lattice/inch.sup.2) was immersed in the
slurry of powder catalyst 1, and taken out. After blowing excessive slurry
off, the support was dried at 200.degree. C. By this procedure 100 g/L of
powder catalyst 1 (first layer catalyst) was coated on the substratate.
Then the support coating with powder catalyst 1 was immersed in the slurry
of powder catalyst 1', and taken out. After blowing excessive slurry off,
the support was dried at 200.degree. C. By this procedure 100 g/L of
powder catalyst 1' (second layer catalyst) was coated.
The catalyst thus obtained was designated as honeycomb catalyst 1.
EXAMPLE 2
Preparation of Catalyst
Except for adding cobalt chloride, ruthenium chloride, rhodium chloride,
lanthanum chloride, cerium chloride, titanium chloride, vanadium chloride,
chromium chloride, antimony chloride, gallium chloride and niobium
chloride in molar amounts as oxides similar to that of Fe.sub.2 O.sub.3
instead ferric chloride used in the synthesis of crystalline silicate 1 in
Example 1, the procedure similar to that employed for crystalline silicate
1 was conducted to obtain crystalline silicates 2 to 12. The crystal
structures of these crystalline silicates as X-ray diffraction patterns
are characterized as shown above in Table A, with the compositions being
represented by the following formula in molar ratios of the oxides
(dehydrated forms): 0.5Na.sub.2 O.0.5H.sub.2 O.(0.2M.sub.2
O.sub.3.0.8Al.sub.2 O.sub.3.0.25CaO).25SiO.sub.2, wherein M denotes Co,
Ru, Rh, La, Ce, Ti, V, Cr, Sb, Ga or Nb.
Except for adding magnesium acetate, strontium acetate and barium acetate
each in the molar amount as an oxide similar to that of CaO instead of
calcium acetate used in the synthesis of crystalline silicate 1 in Example
1, the procedure similar to that employed for crystalline silicate 1 was
conducted to obtain crystalline silicates 13 to 15. The crystal structures
of these crystalline silicates as X-ray diffraction patterns were shown
above in Table A, with the compositions being represented by the following
formula in molar ratios of the oxides (dehydrated forms): 0.5Na.sub.2
O.0.5H.sub.2 O.(0.2Fe.sub.2 O.sub.3.0.8Al.sub.2
O.sub.3.0.25MeO).25SiO.sub.2, wherein Me denotes Mg, Sr or Ba.
Using crystalline silicates 2 to 15 and the procedure similar to that
employed in Example 1, silicates of type H were obtained and then immersed
in the aqueous solution of chloroiridic acid to obtain powder catalysts 2'
to 15'.
Preparation of Honeycomb Catalysts
Each of powder catalysts 2' to 15' was processed similarly as in Example 1
to form slurries, which were used as the second layer catalyst and coated
instead of the slurry of powder catalyst 1' at the rate of 100 g/L onto
the surface of the support which had already been coated with powder
catalyst 1. The catalysts thus obtained were designated as honeycomb
catalysts 2 to 15.
EXAMPLE 3
.gamma.-Al.sub.2 O.sub.3, .theta.-Al.sub.2 O.sub.3, SiO.sub.2, ZrO.sub.2,
TiO.sub.2, Al.sub.2 O.sub.3.ZrO.sub.2 (1:1 by weight), ZrO.sub.2.TiO.sub.2
(1:1 by weight), Al.sub.2 O.sub.3. TiO.sub.2 (1:1 by weight), SO.sub.4
/ZrO.sub.2, zeolite of type Y, silicalite, zeolite of type A, and
mordenite instead of crystalline silicate 1 used in Example 1 were
immersed in and impregnated with the aqueous solution of chloroiridic acid
solution similarly as in Example 1 to obtain powder catalysts 16' to 28'.
Then, each of powder catalysts 16' to 28' was processed similarly as in
Example 1 to form slurries, which were used as the second layer catalyst
and coated instead of the slurry of powder catalyst 1' at the rate of 100
g/L onto the surface of the support which had already been coated with
powder catalyst 1. The catalysts thus obtained were designated as
honeycomb catalysts 16 to 28.
EXAMPLE 4
Instead of the aqueous solution of chloroplatinic acid used in the
preparation of powder catalyst 1 in Example 1, 100 g of .gamma.-alumina
was immersed in each of aqueous solutions of rhodium chloride
(RhCl.sub.3.3H.sub.2 O: 1.45 g/100 cc) or palladium chloride
(PdCl.sub.2.2H.sub.2 O: 1.10 g/100 cc), mixed aqueous solutions of
chloroplatinic acid rhodium chloride (H.sub.2 PtCl.sub.6.6H.sub.2 O: 1.33
g+RhCl.sub.3.3H.sub.2 O: 0.73 g/100 cc), mixed aqueous solutions of
chloroplatinic acid.palladium chloride (H.sub.2 PtCl.sub.6.6H.sub.2 O:
1.33 g+PdCl.sub.2.2H.sub.2 O: 0.55 g/100 cc) and mixed aqueous solutions
of chloroplatinic acid.rhodium chloride.palladium chloride (H.sub.2
PtCl.sub.6.6H.sub.2 O: 0.89 g+RhCl.sub.3.3H.sub.2 O: 0.48
g+PdCl.sub.2.2H.sub.2 O: 0.37 g/100 cc), kept at 120.degree. C.,
evaporated to dryness, and then purged with nitrogen for 3 hours at
500.degree. C. to obtain powder catalysts 2 to 6
Then, each of powder catalysts 2 to 6 was processed similarly as in Example
1 to form slurries, which were used as the first layer catalyst and coated
instead of powder catalyst 1 at the rate of 100 g/L onto the surface of
the support in a manner similar to that employed in Example 1, and then
powder catalyst 1' was coated as an overlayer similarly as in Example 1.
The catalysts thus obtained were designated as honeycomb catalysts 29 to
33.
EXAMPLE 5
Crystalline silicate 1 of type H in Example 1 was employed instead of
.gamma.-alumina for powder catalyst 1 in Example 1 and immersed in the
aqueous solution of chloroplatinic acid similarly as in Example 1 to
obtain powder catalyst 7. Powder catalyst 7 as the first layer catalyst
and powder catalyst 1' as the second layer catalyst were processed
similarly as in Example 1 to obtain honeycomb catalyst 34.
COMPARATIVE EXAMPLE 1
Only powder catalyst 1 was coated onto a honeycomb elemental support at the
rate of 200 g/L similarly as in Example 1 to obtain honeycomb catalyst 35.
Compositions of the inventive and comparative catalysts described above are
shown in Table B.
TABLE B
__________________________________________________________________________
1st layer catalyst powder
2nd layer catalyst powder
Honeycomb
Active Active
catalyst
No
metal
Carrier composition
No
metal
Carrier composition
__________________________________________________________________________
1 1 Pt .gamma.-Al.sub.2 O.sub.3
1'
Ir 0.5Na.sub.2 O.0.5H.sub.2 O (0.2Fe.sub.2
O.sub.3.0.8Al.sub.2 O.sub.3.0.25CaO)
2 1 Pt .gamma.-Al.sub.2 O.sub.3
2'
Ir 0.5Na.sub.2 O.0.5H.sub.2 O (0.2Co.sub.2
O.sub.3.0.8Al.sub.2 O.sub.3.0.25CaO)
3 1 Pt .gamma.-Al.sub.2 O.sub.3
3'
Ir 0.5Na.sub.2 O.0.5H.sub.2 O (0.2Ru.sub.2
O.sub.3.0.8Al.sub.2 O.sub.3.0.25CaO)
4 1 Pt .gamma.-Al.sub.2 O.sub.3
4'
Ir 0.5Na.sub.2 O.0.5H.sub.2 O (0.2Rh.sub.2
O.sub.3.0.8Al.sub.2 O.sub.3.0.25CaO)
5 1 Pt .gamma.-Al.sub.2 O.sub.3
5'
Ir 0.5Na.sub.2 O.0.5H.sub.2 O (0.2La.sub.2
O.sub.3.0.8Al.sub.2 O.sub.3.0.25CaO)
6 1 Pt .gamma.-Al.sub.2 O.sub.3
6'
Ir 0.5Na.sub.2 O.0.5H.sub.2 O (0.2Ce.sub.2
O.sub.3.0.8Al.sub.2 O.sub.3.0.25CaO)
7 1 Pt .gamma.-Al.sub.2 O.sub.3
7'
Ir 0.5Na.sub.2 O.0.5H.sub.2 O (0.2Ti.sub.2
O.sub.3.0.8Al.sub.2 O.sub.3.0.25CaO)
8 1 Pt .gamma.-Al.sub.2 O.sub.3
8'
Ir 0.5Na.sub.2 O.0.5H.sub.2 O (0.2V.sub.2
O.sub.3.0.8Al.sub.2 O.sub.3.0.25CaO)
9 1 Pt .gamma.-Al.sub.2 O.sub.3
9'
Ir 0.5Na.sub.2 O.0.5H.sub.2 O (0.2Cr.sub.2
O.sub.3.0.8Al.sub.2 O.sub.3.0.25CaO)
10 1 Pt .gamma.-Al.sub.2 O.sub.3
10'
Ir 0.5Na.sub.2 O.0.5H.sub.2 O (0.2Sb.sub.2
O.sub.3.0.8Al.sub.2 O.sub.3.0.25CaO)
11 1 Pt .gamma.-Al.sub.2 O.sub.3
11'
Ir 0.5Na.sub.2 O.0.5H.sub.2 O (0.2Ga.sub.2
O.sub.3.0.8Al.sub.2 O.sub.3.0.25CaO)
12 1 Pt .gamma.-Al.sub.2 O.sub.3
12'
Ir 0.5Na.sub.2 O.0.5H.sub.2 O (0.2Nb.sub.2
O.sub.3.0.8Al.sub.2 O.sub.3.0.25CaO)
13 1 Pt .gamma.-Al.sub.2 O.sub.3
13'
Ir 0.5Na.sub.2 O.0.5H.sub.2 O (0.2Fe.sub.2
O.sub.3.0.8Al.sub.2 O.sub.3.0.25MgO)
14 1 Pt .gamma.-Al.sub.2 O.sub.3
14'
Ir 0.5Na.sub.2 O.0.5H.sub.2 O (0.2Fe.sub.2
O.sub.3.0.8Al.sub.2 O.sub.3.0.25SrO)
15 1 Pt .gamma.-Al.sub.2 O.sub.3
15'
Ir 0.5Na.sub.2 O.0.5H.sub.2 O (0.2Fe.sub.2
O.sub.3.0.8Al.sub.2 O.sub.3.0.25BaO)
16 1 Pt .gamma.-Al.sub.2 O.sub.3
16'
Ir .gamma.-Al.sub.2 O.sub.3
17 1 Pt .gamma.-Al.sub.2 O.sub.3
17'
Ir .theta.-Al.sub.2 O.sub.3
18 1 Pt .gamma.-Al.sub.2 O.sub.3
18'
Ir SiO.sub.2
19 1 Pt .gamma.-Al.sub.2 O.sub.3
19'
Ir ZrO.sub.2
20 1 Pt .gamma.-Al.sub.2 O.sub.3
20'
Ir TiO.sub.2
21 1 Pt .gamma.-Al.sub.2 O.sub.3
21'
Ir Al.sub.2 O.sub.3.ZrO.sub.2 (1:1)
22 1 Pt .gamma.-Al.sub.2 O.sub.3
22'
Ir ZrO.sub.2.TiO.sub.2 (1:1)
23 1 Pt .gamma.-Al.sub.2 O.sub.3
23'
Ir Al.sub.2 O.sub.3.TiO.sub.2 (1:1)
24 1 Pt .gamma.-Al.sub.2 O.sub.3
24'
Ir SO.sub.4 /ZrO.sub.2
25 1 Pt .gamma.-Al.sub.2 O.sub.3
25'
Ir Zeolite type Y
26 1 Pt .gamma.-Al.sub.2 O.sub.3
26'
Ir Silicalite
27 1 Pt .gamma.-Al.sub.2 O.sub.3
27'
Ir Zeolite type A
28 1 Pt .gamma.-Al.sub.2 O.sub.3
28'
Ir Mordenite
29 2 Rh .gamma.-Al.sub.2 O.sub.3
1'
Ir 0.5Na.sub.2 O.0.5H.sub.2 O (0.2Fe.sub.2
O.sub.3.0.8Al.sub.2 O.sub.3.0.25CaO)
30 3 Pd .gamma.-Al.sub.2 O.sub.3
1'
Ir 0.5Na.sub.2 O.0.5H.sub.2 O (0.2Fe.sub.2
O.sub.3.0.8Al.sub.2 O.sub.3.0.25CaO)
31 4 Pt, Rh
.gamma.-Al.sub.2 O.sub.3
1'
Ir 0.5Na.sub.2 O.0.5H.sub.2 O (0.2Fe.sub.2
O.sub.3.0.8Al.sub.2 O.sub.3.0.25CaO)
32 5 Pt, Pd
.gamma.-Al.sub.2 O.sub.3
1'
Ir 0.5Na.sub.2 O.0.5H.sub.2 O (0.2Fe.sub.2
O.sub.3.0.8Al.sub.2 O.sub.3.0.25CaO)
33 6 Pt, Rh, Pd
.gamma.-Al.sub.2 O.sub.3
1'
Ir 0.5Na.sub.2 O.0.5H.sub.2 O (0.2Fe.sub.2
O.sub.3.0.8Al.sub.2 O.sub.3.0.25CaO)
34 7 Pt Similar as in 2nd
1'
Ir 0.5Na.sub.2 O.0.5H.sub.2 O (0.2Fe.sub.2
O.sub.3.0.8Al.sub.2 O.sub.3.0.25CaO)
layer support
35 1 Pt .gamma.-Al.sub.2 O.sub.3
Similar to the left
__________________________________________________________________________
Honeycomb catalysts 1 to 35 obtained in Examples 1, 2, 3, 4 and 5 and
Comparative 1 were examined for the activity. The results are shown below.
Gas Composition
NO: 500 ppm, CO: 1000 ppm, C.sub.2 H.sub.4 : 1500 ppm, O.sub.2 : 8%,
CO.sub.2 : 10%, H.sub.2 O: 10%, Balance: N.sub.2, GHSV: 30000 h.sup.-1,
Catalyst dimension: 15 mm.times.15 mm.times.60 mm (144 cells)
The denitration rates of the catalysts in the initial state at the inlet
gas temperatures of 250.degree. C. and 350.degree. C. are shown in Table
C.
TABLE C
______________________________________
Inlet exhaust gas Inlet exhaust gas
temperature: 250.degree. C.
temperature: 350.degree. C.
Catalyst Catalyst
Honey- layer NOx layer NOx
comb temperature
decomposition
temperature
decomposition
catalyst
(.degree.C.)
rate (%) (.degree.C)
rate (%)
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1 320 68 420 54
2 315 65 418 58
3 320 68 424 61
4 315 64 423 60
5 320 65 422 63
6 315 62 423 61
7 317 61 422 60
8 320 63 425 59
9 315 65 430 58
10 320 67 419 60
11 317 62 418 59
12 315 60 416 61
13 317 61 417 59
14 314 63 415 60
15 315 65 4i4 61
16 310 60 415 60
17 309 61 414 58
18 312 63 413 60
19 314 59 412 58
20 315 61 415 57
21 316 63 416 60
22 319 65 418 54
23 318 64 416 56
24 320 67 417 58
25 322 68 418 54
26 328 65 420 56
27 319 65 418 54
28 318 66 420 52
29 317 51 423 54
30 314 48 430 51
31 315 49 423 54
32 320 47 420 56
33 321 49 418 54
34 315 65 413 60
35 250 1 419 54
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Honeycomb catalysts 1 to 34 according to the present invention shown in
Table C had a sufficient denitration activity even at a low gas
temperature of approximately 250.degree. C., indicating that they can keep
a high denitration activity over a wide range of temperatures. In
contrast, a comparative catalyst 35 did not show an effective denitration
activity at a low temperature of approximately 250.degree. C.
Honeycomb catalysts 1 to 34 according to the present invention had stable
activity in a reducing atmosphere also at a high temperature of
approximately 700.degree. C., thus ensuring high durability.
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